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<span id="ATAN2D"></span><div class="header">
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<span id="ATAN2D-_002d_002d_002d-Arctangent-function_002c-degrees"></span><h3 class="section">8.26 <code>ATAN2D</code> &mdash; Arctangent function, degrees</h3>
<span id="index-ATAN2D"></span>
<span id="index-DATAN2D"></span>
<span id="index-trigonometric-function_002c-tangent_002c-inverse_002c-degrees-1"></span>
<span id="index-tangent_002c-inverse_002c-degrees-1"></span>

<dl compact="compact">
<dt><em>Description</em>:</dt>
<dd><p><code>ATAN2D(Y, X)</code> computes the principal value of the argument
function of the complex number <em>X + i Y</em> in degrees.  This function can
be used to transform from Cartesian into polar coordinates and
allows to determine the angle in the correct quadrant.
</p>
<p>This function is for compatibility only and should be avoided in favor of
standard constructs wherever possible.
</p>
</dd>
<dt><em>Standard</em>:</dt>
<dd><p>GNU extension, enabled with <samp>-fdec-math</samp>.
</p>
</dd>
<dt><em>Class</em>:</dt>
<dd><p>Elemental function
</p>
</dd>
<dt><em>Syntax</em>:</dt>
<dd><p><code>RESULT = ATAN2D(Y, X)</code>
</p>
</dd>
<dt><em>Arguments</em>:</dt>
<dd><table>
<tr><td width="15%"><var>Y</var></td><td width="70%">The type shall be <code>REAL</code>.</td></tr>
<tr><td width="15%"><var>X</var></td><td width="70%">The type and kind type parameter shall be the same as <var>Y</var>.
If <var>Y</var> is zero, then <var>X</var> must be nonzero.</td></tr>
</table>

</dd>
<dt><em>Return value</em>:</dt>
<dd><p>The return value has the same type and kind type parameter as <var>Y</var>. It
is the principal value of the complex number <em>X + i Y</em>.  If <var>X</var>
is nonzero, then it lies in the range <em>-180 \le \atan (x) \leq 180</em>.
The sign is positive if <var>Y</var> is positive.  If <var>Y</var> is zero, then
the return value is zero if <var>X</var> is strictly positive, <em>180</em> if
<var>X</var> is negative and <var>Y</var> is positive zero (or the processor does
not handle signed zeros), and <em>-180</em> if <var>X</var> is negative and
<var>Y</var> is negative zero.  Finally, if <var>X</var> is zero, then the
magnitude of the result is <em>90</em>.
</p>
</dd>
<dt><em>Example</em>:</dt>
<dd><div class="example">
<pre class="example">program test_atan2d
  real(4) :: x = 1.e0_4, y = 0.5e0_4
  x = atan2d(y,x)
end program test_atan2d
</pre></div>

</dd>
<dt><em>Specific names</em>:</dt>
<dd><table>
<thead><tr><th width="23%">Name</th><th width="23%">Argument</th><th width="20%">Return type</th><th width="30%">Standard</th></tr></thead>
<tr><td width="23%"><code>ATAN2D(X, Y)</code></td><td width="23%"><code>REAL(4) X, Y</code></td><td width="20%"><code>REAL(4)</code></td><td width="30%">GNU extension</td></tr>
<tr><td width="23%"><code>DATAN2D(X, Y)</code></td><td width="23%"><code>REAL(8) X, Y</code></td><td width="20%"><code>REAL(8)</code></td><td width="30%">GNU extension</td></tr>
</table>

</dd>
<dt><em>See also</em>:</dt>
<dd><p>Alias: <br>
<a href="ATAND.html">ATAND</a> <br>
Radians function: <br>
<a href="ATAN2.html">ATAN2</a>
</p></dd>
</dl>



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